1. Field of the Invention
The present invention relates generally to an electrical wheelchair, and in particular to an anti-turnover mechanism of an electrical wheelchair for operation safety purposes.
2. The Related Art
The improvement of technology and medical care extends life of human beings. The old and the disabled are best benefited from the modern technology and medical care. A lot of different supportive devices have been developed for helping the old and the disabled to transport themselves in an extended area so as to improve their living standard without particular care by other supporting medical personnel. Wheelchairs have been one of the most commonly known supportive devices for the old and the disabled to transport themselves in short distances. However, for those very weak or those having hand or arm injured, they still need other people""s help in moving the wheelchairs.
Electrical wheelchairs that are equipped with electrical motors allows a person to drive the wheelchair without great effort and thus are particularly suitable for those whose arms are weak or injured. The electrically powered wheelchairs are also advantageous as compared with vehicles equipped with engines powered by fossil fuels for environmental protection.
The electrical wheelchair comprises two wheels to which electrical motors are mechanically coupled and two front casters for guiding the moving direction of the wheelchair. To ensure a sitter""s safety, the electrical wheelchair is equipped with anti-turnover mechanism, which is usually comprised of two rear casters, to prevent turnover of the electrical wheelchair when moving on an uneven road or surface. Climbing over a step-like raised surface is one of the most commonly seen challenges for the wheelchair moving in the uneven road. In climbing over a step, the front casters are moved to the raised top surface of the step first, while the wheels are still on the lower surface, or in moving down the step, the front casters are moved to the lower surface first with the wheel still positioned on the raised top surface of the step. In both situations, the wheelchair is tilted. For raised surfaces of limited heights, the tilting of the wheelchair is within a range wherein the gravity center of the wheelchair is located in the projected bottom area of the wheelchair and turnover of the wheelchair is prevented. However, for a raised surface of a substantial height, attempting to climb over the step may cause turnover of the wheelchair. Thus, anti-turnover mechanism is required for the electrical wheelchair for safety purposes.
FIG. 15 of the attached drawings shows a conventional electrical wheelchair with anti-turnover mechanism. The conventional electrical wheelchair, which is designated with reference numeral 10, comprises a chassis 12 on which a seat 14 is mounted. Two wheels 16 are mounted on opposite sides of the chassis 12 and are coupled to electrical driving units 18, which are often electrical motors, to drive the wheelchair 10 forward and/or backward. The motors 18 are fixed in the chassis 12 and are controlled by a control unit 20 that is located in front of the seat 14 for ready access of a sitter of the wheelchair 10. Two front casters 22 are mounted on the front side of the chassis 12 for smooth movement of the wheelchair 10 and for controlling moving direction of the wheelchair 10.
Two rods 24 that are spaced from each other extend rearward from the chassis 12. A rear caster or anti-turnover roller 26 is rotatably supported by each of the rods 24. The rear caster 26 is in general not contacting the surface of a road when the wheelchair 10 is moving on a substantially flat road. When the wheelchair is climbing a raised surface which causes the chassis 12 to tilt rearward, the rear casters 26 contact the ground surface and prevent undesired over-tilting situation. Thus turnover of the wheelchair 10 is effectively eliminated.
Conventionally, the relative position of the rear casters 26 with respect to the chassis 12 is fixed. In other words, the angle of rearward tilting of the chassis 12 that is allowed by the rear casters 26 is limited, determined by the relative position of the rear casters 26 with respect to the chassis 12. This imposes a constraint to the height of the raised surfaces that the wheelchair can climb.
Furthermore, the rear casters 26 of the conventional electrical wheelchair 10 are not capable to absorb shock caused by dropping down a step-like raised surface. In moving the wheelchair 10 down a step-like raised surface, the wheels 16 often drop down suddenlyl with the rear casters 26 hitting the top surface of the step. This causes an uncomfortable shock to the sitter of the wheelchair.
It is thus desirable to have an electrical wheelchair that overcomes the above problems.
An object of the present invention is thus to provide a wheelchair having an anti-turnover mechanism that allows the electrical wheelchair to climb over raised surfaces of different heights without causing turnover of the wheelchair.
Another object of the present invention is to provide a wheelchair that is provided with shock absorbing device for absorbing shock caused by moving down a raised surface.
A further object of the present invention is to provide a wheelchair that is provided with energy storing device that stores energy in an initial phase in climbing a raised surface and releases the energy for helping climbing the raised surface in a final phase of the climbing so as to ensure safe and effective operation of the wheelchair in climbing of the raised surface.
To achieve the above objects, in accordance with the present invention, there is provided an electrical wheelchair comprising a chassis to which a frame is pivotally mounted. Two casters are rotatably mounted to the frame. At least a resilient member is arranged between the frame and the chassis for supporting the relative position of the frame with respect to the chassis. The resilient member is deformable to change the relative position of the frame with respect to the chassis for allowing the wheelchair to climb over raised surfaces of different heights. The deformation of the resilient member stores energy therein which may be released when the wheelchair is about to reach the raised surface for enhancing the movement of the wheelchair over the raised surface. Further, the resilient member also functions to absorb shock caused by the wheelchair moving down a step-like raised surface.